1. Field of the Invention
The present invention relates to a navigation system for carrying out a navigation operation by using map data which is recorded in a record medium, and more particularly relates to a navigation system, which can selectively read the map data from a plurality of memory devices each capable of reading out the map data.
2. Description of the Related Art
There is a navigation system, which has a DVD-ROM (DVD-Read Only Memory) drive or a CD-ROM (Compact Disc—Read Only Memory) drive, reads map data stored in a DVD-ROM or a CD-ROM as a record medium, and carries out a navigation operation. When carrying out the navigation operation, the navigation system detects a self-car position, reads the map data around the car from the record medium, and then displays a map picture generated on the basis of the map data together with a mark indicative of the self-car position on a display screen.
On the other hand, it may be considered that the navigation system is equipped with, for example, a hard disc, as a non-volatile memory having a large capacity, besides the record medium. If the map data of the DVD-ROM or the like is installed in the hard disc, and then the map data is read from the hard disc at a time of the navigation operation, the DVD-ROM or the like can be used for another purpose. Also, since an access speed for the hard disc is very fast, this has a merit from the viewpoint of a fast drawing on a display screen.
By the way, a record medium such as a DVD-ROM or the like is available in which music data and video data are recorded in a format of DVD-Video or DVD-Audio. Thus, it is desired to perform a reproduction of such a record medium during a car driving operation. However, the above-mentioned navigation system requires that the record medium in which the map data is stored is always inserted in the DVD-ROM drive or the like during the navigation operation. Namely, the DVD-ROM drive or the like is occupied by the record medium for the navigation operation. Hence, it is difficult to use the DVD-ROM drive or the like for another purpose such as a reproduction of the music data or video data.
On the other hand, it may be considered that the navigation system is equipped with, for example, a hard disc, as a non-volatile memory having a large capacity, besides the record medium. If the entire data of the DVD-ROM or the like is perfectly installed in the hard disc, and then the map data is read from the hard disc at a time of the navigation operation, the DVD-ROM or the like can be used for another purpose. Also, since an access speed for the hard disc is very fast, this has a merit from the viewpoint of a fast drawing on a display screen.
However, if the navigation system is constructed such that the map data can be selectively read from one of the hard disc and the DVD-ROM or the like, there may be a possibility that the map data for the same area redundantly exist in both of them. At this time, the data contents of the map data stored in them may not be same to each other. For example, there may be a case that the latest map data is stored in the DVD-ROM while the old map data stored in the past is still maintained in the hard disc without updating. In such a case, if the old map data is used for the navigation, a situation may arise that the map data does not reflect the actual road circumstance around the self-car, resulting in that the appropriate navigation cannot be performed.
Further, even if the navigation system is constructed such that the map data can be selectively read from one of the hard disc and the DVD-ROM or the like, the user may want to use the DVD-ROM or the like, in which the special version of map data including useful information is stored, to thereby perform the navigation.
In this manner, even if the map data can be read from a plurality of memory devices, it is difficult to select the optimum memory device from among them and then read the map data from the selected memory device.